Hi SilentBang!
One thing about Lua script that is really beneficial is to look over the examples that come with the engine. I didn't know anything about Lua scripting until I looked at these scripts, and they should start to make sense as you play around with them a little. There are a lot of resources as well on the web since Lua scripting is popular among the modding community as well. Personally, I don't think you would need to buy a book, but if you want that's up to you. It also depends on how much experience you have with programming as well. Plus, the community here is very helpful!
As for making better maps, that's sort of a vague topic. I'm sure there are level design tutorials online as well, but if you are looking to make realistic terrain or something, I would recommend using a heightmap generator.